B2.1 Membrane and Membrane Transport

Definition of amphipathic and examples

• contains both hydrophobic and hydrophillic parts

• example: cholesterol and phoslipids

draw the strucutre of one phospholid. label: hydrophobic/hydrophillic, polarity, components, etc

how are the phospholipids bilayers held together?

by hydrophobic interactions of the tails

a phospholipid bilayer is formed ___ as a ___ sheet in ___

a phospholipid bilayer is formed naturally as a continuous sheet in water

the phospholipid bilayer acts as a ____ between ___ ___, allowing for ___

the phospholipid bilayer acts as a barriar between aqueous solutions, allowing for compartmentalisation

List the permeability of the hydrophobic tails to different molecules

permeable: non-polar, lipid-soluble moelcules (e.g. O2, CO2)

semi-permeable: small polar molecules (e.g. H2O)

impermeable: large polar moleucles (e.g. glucose), ions (e.g. Na+)

Explain the process of Simple Diffusion

• passive transport

• from high conc to low conc, along the CG

• movment of small, non-polar molecules (e.g. O2, CO2)

• not selective

• squeezes through the phospholipid heads

• occurs because of molecular collisions towards the bilayer

Explain the process of Facilitated Diffusion

• passive transport using a channel protein

• along the CG, from high conc to low conc

• movement of large, polar molecules (e.g. glucose) and ions (e.g. Na+)

• when open: allows specific ions to diffuse through (selective permeability)

• when closed: stops diffusion

• allows for selective permeability due to manipulation of open and close

2 types of membrane proteins and describe their formation/ polarity

Integral protein

• embedded into one or both bilayers

• amphipathic, thus can extend into the bilayer

• function determines how they are embedded in the membrane

peripheral proteins

• attached to only one surface (inner or outer of the cell) of the bilayer

• is not amphipathic

5 functions/ types of membrane proteins

structural (1-3), functional (4-5)

1. extracellular matrix, cytoskeletal anchors

2. enzymes

3. receptors (e.g. hormones)

4. passive transporters

5. active transporters

Osmosis

• passive diffusion of H2O across a semi-permeable membrane

• from low solute conc to high solute conc.

• until equilibrium is reached

• only the solvent is permeable to the membrane, solutes are not.

Aquaporins

• a water channel protein

• integral/ transmembrane protein that rapidly transports H2O

• H2O is semi permeable, so it needs faciliation

• lining of the aquaporin is polar (lined with hydrophillic side chains)

Active transport

• pump proteins that use ATP to move specific particles against their CG (from low conc to high conc)

• allows for membrane selective permeability

Cell adhesion

identify self VS self

cell recognition

identify self VS foreign

glycoproteins and its role

• short carbohydrate chain (oligosaccharide) attached to proteins on the extracellular surface.

• responsible for facilitating cell adhesion and recognition

Fluid Mosaic Model (REQUIRED DRAWING)

• peripheral and integral proteins

• glycoproteins

• phospholipid bilayer

• cholesterol

• hydrophobic and hydrophillic regions labeled

ectotherms and hibernating organisms usage of cell membrane

• e.g. fishes, reptiles, frogs

• in cold temp, membrane is at risk of being too rigid

• adapts to low temp by maintainin fluidity of cell membrane by increase # of unsaturated fatty acids

endotherms do not need this becuase the internal temp of endotherms are built to maintain homeostasis. ectotherms mimic the environment.

cholesterol

• an amphipathic steroid

  • hydrophobic section to the tail

  • hydrophillic section to the head

• only in animal cells

• presence result in more space between phospholipids —> maintain fluidity in low temp env

• acts as an anchor and stabalises membrane at high temp env by connecting the phospholipids

endocytosis/ exocytosis

• invaginate, engulf, pinch, fuse

• this is also only possible becasuse vesicle and plasma membrane are made of the same phospholipid bilayer

explain process of sodium potassium pump

• direct active transport

• transport Na+ and K+ against the CG

• exchange transport of:

  • Na+ exits cell

  • K+ enters cell

and more… (hydrolysis of ATP, number of binding sites, conformational changes…)

Outline what Indirect active transport is.

• usage of a cotransporter protein/ symporter

• simulatenously: one solute along its CG, driving the other solute against its CG

• use a active transport pump to establish a gradient of one of the solutes (e.g. Na+)

Explain the sodium dependent glucose cotransporter/ Na+ glucose symporter

• on microvilli of epithelial cells int he lining of the small intestine, aids the absorption of glucose

• Na+ pump sets [Na+] gradient of low [Na+] inside and high [Na+] by pumping Na+ outside using ATP

• 2 Na+ outside binds to 2 binding sites on the sympoter while 1 glucose binds to 1 binding site on the symporter

• Na+ moves along its CG from outside (high [Na+]) to insided (low [Na+])

• while glucose moves against its CG from outside (low conc) to inside (high conc) using the energy generated by Na+ going along its CG

describe what CAMs (cell-adhesion molecules) are.

• glycoproteins (carb chain of olgiosaccharide + a membrane protein)

• faciliates cell adhesion

describe what cell-cell junctions are

• connections that allow cells to communicate with one another with transport

• has 3 types

state what the 3 types of cell-cell junctions are

1. gap junctions: transfer of molecules

2. tight junctions: seal that prevents movement or leakeage of certain molecules

3. adhesive junctions: structural stability

There exist diff types of ___ for diff types of cell-cell junctions

There exist diff types of CAMs for diff types of cell-cell junctions